Find the missing fraction.
Answer: Let's look at the multiples of each denominator and see which multiples they have in common. Denominator Multiples ${10}$ $\underline{{10}}, 20, 30$ ${5}$ $5, \underline{{10}}, 15$ The least common multiple is ${10}$. Let's use multiplication to make ${\dfrac{1}{5}}$ have a denominator of $10$. ${\dfrac{1}{5}}=\dfrac{{1} \times 2}{{5} \times 2} = {\dfrac{2}{10}}$ So, $\boxed{\phantom{\dfrac14}} - {\dfrac3{10}}= {\dfrac{2}{10}}$ $\dfrac{3}{10}$ $\dfrac{2}{10}$ $\boxed{\phantom{{\dfrac{5}{10}}}}$ $\boxed{{\dfrac{5}{10}}} - {\dfrac3{10}}= {\dfrac{2}{10}}$ $\dfrac{3}{10}$ $\dfrac{2}{10}$ ${\dfrac{5}{10}}$ $\boxed{{\dfrac{5}{10}}} - {\dfrac{3}{10}} = {\dfrac{1}{5}}$ ${\dfrac{5}{10}}$ can also be written as ${\dfrac{1}{2}}$.